1. Field of the Invention
The present invention relates to a method of production of a zinc cysteate, its preparation and uses in pharmacy and cosmetology.
2. Brief Description of the Background of the Invention Including Prior Art
Mixtures containing various constituents, where possibly various metals, susceptible to chelate the cysteic acid, are added to the cysteic acid, are taught in the U.S. Patent No. 4,224,339 to Van Scott et al. In this reference a salt is a composition comprising a negative anion and a positive cation which are bonded to each-other by a heteropolar bond and where this heteropolar bond disappears during the dissolution, for example in water, and creates thus two ions, the anion and the cation, which is, in this case, the cysteic acid ion and the zinc cation. A chelate on the other hand is a chemical entity, wherein a metal is bonded to another molecule or ion, which is in general organic, by a covalent bonding process or by coordination based on free electron pairs of the one and the holes of the second atom.
The invention zinc cysteate is a salt composed of two ions which are bonded by heteropolar forces. In contrast, the U.S. Pat. No. 4,224,339 requires the presence of chelates, where the metals are bonded to the remainder of the molecule by covalent forces or coordination forces.
The existence of zinc was recognized in biology more than a century ago and the book of Jean Lederer "Le zinc en Pathologie et en Biologie" (Zinc in Pathology and Biology) published by Nauwelaerts in Brussels (1985) is an abstract of up-to-date knowledge about the subject.
Olivier Guillard teaches in his thesis "Metabolism of a New Zinc Pantothenate" for the Degree of Doctor of Pharmacy, Poitiers University, 1978, that the zinc salt of 2-pyridine-thione is used in many hair lotions against dandruff.
Zinc is essential for growth and multiplication of cells and a deficiency in zinc impairs the cicatrization of wounds. However, A. Favier at al. teach in the publication Lyon Pharmaceutiques, 1980, 31, 6, pp. 357-366, that in a normal animal, i.e. without zinc deficiency, extra zinc does not accelerate the cicatrization.
Then it is quite surprising that the new salt of the present invention, zinc cysteate, has peculiar cicatrizing qualities, all the more because the organic anion of the salt, cysteic acid, is unknown for this therapeutic use, moreover because its sulfur function is in an oxidized form.
As a matter of fact, scientific literature learns that it is in the reduced form of mercaptan that sulfur compounds, for instance glutathione, are cicatrizing agents.
It is known in the art that zinc cysteate and cysteic acid are two different compositions and that each of these two compositions can crystallize in water with a number of associated molecules of water of hydration.
If a hydride is heated, it will lose its water above a critical temperature. A person of ordinary skill in the art knows that the dihydrate obtained by concentration of an aqueous solution or by recrystallization in water can be separated and dried at 30.degree. to 40.degree. C. Such a mild drying temperature is used because at a higher temperature the two water molecules of crystallization start to evaporate and this occurs at ordinary pressure. The anhydrous salt is obtained by heating to 105.degree. C. at ambient pressure. The organic salts generally lose their crystallization water before this temperature is attained. This is used to a very large extent in pharmaceutical preparations for evaluation of the loss occurring during drying based on which one measures in particular the number of the water molecules in the hydrated crystals. Therefore, a drying has to take place at 105.degree. C. in order to obtain an anhydrous product.
The hydration of CB 619 in salt form, where CB 619 is the code name of the dihydrated zinc cysteate, occurs in that the number of associated water molecules is calculated by the weight difference between the hydrated product, dried at a temperature of 30.degree. to 40.degree. C. as indicated, and the same product dried to a constant weight at a higher temperature, in particular at a temperature of 105.degree. C. as indicated above.
For example, if the weights Pa and Pb before and after drying, and if M is the molecular weight of the anhydrous salt, the number N of the water, molecules associated to each salt molecule is furnished by the following formula: EQU N=M(Pa-Pb)/18 Pb.